a) Technical Field
The invention is directed to a method for the automatic supply of bags for packing bulk material by means of positive guidance of the bags from a bag stack, opening the bag filling opening, and hanging the open end of the bag at a filling sleeve.
b) Background Art
U.S. Pat. No. 3,566,578 shows an automatic hanging of shipping bags such as was suggested at the inception of automation. The basic idea is simple. A whole stack of paper bags is put on a conveyor belt in the correct position as close as possible to the filling sleeve and each individual paper bag is attached via an automatic gripper with suction cups to the bag filling sleeve which is provided with a bag opening and holding device which likewise works automatically. Such a device is easily capable of hanging several hundred bags per hour at the filling sleeve, an operation which over a longer period of time would degrade a person to a robot and which could be withstood by this person over the course of an entire day only with the greatest effort. When such automatic devices were introduced, it was already known that a natural product such as paper can have different, often even unpleasant, behavior.
The most common disturbing factor is moisture in the air and in the material. Often a bag cannot be opened at all with the given mechanical means, or two bags are lifted by the automatic grippers simultaneously.
Over the course of time this state of affairs was tolerated since it was necessary in any case, due to completely different problems, e.g. the bursting of full bags, for a supervisor to monitor the entire packing operation and to ensure order as well as provide for a smooth feed of bags. A noticeable increase in hourly output was not possible since a more rapid sequence of movements simultaneously increased the frequency of disturbances so that ultimately an increase in output calculated over the course of a day did not occur.
Opening the bag in a problem-free manner remained a principle weak point. In U.S. Pat. No. 4,320,615, the present applicant attempted to overcome both disadvantages of the older solutions. As was shown in FIGS. 2a, 2b and 2c of this patent, it was possible, by means of a simultaneous rolling process, to prepare the opening of a bag while lifting the bag and to almost completely prevent a second or third bag from being carried along. In this way approximately 600 to 800 bags per hour could be hung and disturbances were sharply reduced.
For a long time, the prevailing opinion in technical circles was that it was substantially more economical to ship larger quantities of mill products to the consumer in a loose state by tank vehicles. A sharp reduction in variety was simultaneously anticipated. But recent trends have now shown that a large variety is demanded.
Further, great advances in automation in the area of palletization of bags have been achieved so that transporting by bags has gained ground again and an increase in the hourly output is demanded in particular.